The storms at the end of August did not recharge the groundwater tables in Brittany. “The drop in groundwater levels continues throughout the region despite some effective summer rains”, indicates the Geological and Mining Research Bureau (BRGM) in a press release, Monday, September 5, 2022. It reports “two thirds of the Breton aquifers showing a falling level”.
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“Small momentary refills”
In Morbihan, southern Finistère and the center of Ille-et-Vilaine, 31% of BRGM’s piezometers (a device that measures the pressure of liquids) recorded stable groundwater levels, a consequence of “effective rains in mid-August and late August which caused small momentary recharges”. A single rising groundwater level is observed at the Baud piezometer, near Pontivy (Morbihan), “where the recharge was locally greater”.
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Rainfall deficit over the last ten months
The BRGM reports a filling of aquifers (soil or rock containing an underground water table) at the end of August 2022 “mainly very low (44% of the piezometers) compared to the averages for the months of August”. This situation, visible in the four Breton departments in particular in Finistère, is explained “by the rainfall deficit of the last 10 months and by the regular emptying of underground reservoirs since February 2022”.
According to the BRGM, from September 2021 to August 2022, precipitation was much lower than normal at the following four stations: 78% of normal at the Rennes Saint-Jacques station (Ille-et-Vilaine), 81% at Saint -Brieuc Trémuson (Côtes-d’Armor), 59% in Pontivy (Morbihan) and 76% in Spézet Saint-Goazerc (Finistère).